The field of art to which this invention pertains is the hydrocracking of a hydrocarbonaceous feedstock. Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel and other products known as middle distillates as well as lower boiling hydrocarbonaceous liquids such as naphtha and gasoline by hydrocracking a hydrocarbon feedstock derived from crude oil, for example. Feedstocks most often subjected to hydrocracking are gas oils and heavy gas oils recovered from crude oil by distillation. A typical atmospheric gas oil comprises a substantial portion of hydrocarbon components boiling above about 260xc2x0 C. (500xc2x0 F.), usually at least about 80 percent by weight boiling above 260xc2x0 C. (500xc2x0 F.). A typical vacuum gas oil normally has a boiling point range between about 315xc2x0 C. (600xc2x0 F.) and about 565xc2x0 C. (1050xc2x0 F.).
Hydrocracking is generally accomplished by contacting in a hydrocracking reaction vessel or zone the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. The operating conditions and the hydrocracking catalysts within a hydrocracking reactor influence the yield of the hydrocracked products.
Although a wide variety of process flow schemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new hydrocracking methods which provide lower costs, higher liquid product yields and better product quality.
U.S. Pat. No. 5,720,872 (Gupta) discloses a process for hydroprocessing liquid feedstocks in two or more hydroprocessing stages, which are in separate reaction vessels and wherein each reaction stage contains a bed of hydroprocessing catalyst. The liquid product from the first reaction stage is sent to a low pressure stripping stage and stripped of hydrogen sulfide, ammonia and other dissolved gases. The stripped product stream is then sent to the next downstream reaction stage, the product from which is also stripped of dissolved gases and sent to the next downstream reaction stage until the last reaction stage, the liquid product of which is stripped of dissolved gases and collected or passed on for further processing. The flow of treat gas is in a direction opposite the direction in which the reaction stages are staged for the flow of liquid. Each stripping stage is a separate stage, but all stages are contained in the same stripper vessel.
U.S. Pat. No. 5,114,562 (Haun et al) discloses a process wherein a middle distillate petroleum stream is hydrotreated to produce a low sulfur and low aromatic product employing two reaction zones in series. The effluent of the first reaction zone is cooled and purged of hydrogen sulfide by stripping and then reheated by indirect heat exchange. The second reaction zone employs a sulfur-sensitive noble metal hydrogenation catalyst. Operating pressure and space velocity increase, and operating temperature decreases from the first to the second reaction zones. The ""562 patent teaches that the hydroprocessing reactions of the hydrodenitrification and hydrodesulfurization will occur with very limited hydrocracking of the feedstock. Also, it is totally undesired to perform any significant cracking within the second reaction zone.
U.S. Pat. No. 3,540,999 (Jacobs) discloses a process for converting heavier hydrocarbonaceous material into jet fuel kerosene and gasoline fractions. The simultaneous production of both jet fuel and gasoline fractions, in maximum quantities, is afforded through the utilization of a modified xe2x80x9cseries-flowxe2x80x9d system. A two-stage process in which the jet fuel kerosene fraction is produced in the first stage with the gasoline fraction being produced in the second stage.
The present invention is a catalytic hydrocracking process, which provides high liquid yields of low sulfur gasoline and ultra low sulfur diesel while simultaneously processing two feedstocks. One preferred feedstock boils in the temperature range of diesel and the second preferred feedstock boils in the temperature range above that of diesel. The process of the present invention is particularly useful in a revamp of an existing maximum naphtha hydrocracker in order to maximize or increase throughput while co-producing ultra low sulfur diesel from two feedstocks.
In accordance with one embodiment, the present invention relates to a hydrocracking process for maximum production of ultra low sulfur diesel which process comprises: (a) contacting a first hydrocarbonaceous feedstock and hydrogen with a hydrotreating catalyst in a first hydrotreating reaction zone at reaction conditions including a temperature from about 204xc2x0 to 482xc2x0 C. (400xc2x0 to 900xc2x0 F.) and a pressure from about 3.6 to 17.3 MPa (500 to 2500 psig) and recovering a hydrotreating reaction zone effluent therefrom; (b) passing at least a portion of the first hydrotreating reaction zone effluent and a hereinafter described liquid hydrocarbonaceous recycle stream to a hydrocracking reaction zone containing hydrocracking catalyst and operated at reaction zone conditions including a temperature from about 204xc2x0 to 482xc2x0 C. (400xc2x0 to 900xc2x0 F.) and a pressure from about 3.6 to 17.3 MPa (500 to 2500 psig) and recovering a hydrocracking reaction zone effluent therefrom; (c) introducing the hydrocracking reaction zone effluent into a high pressure stripper to produce a hydrocarbonaceous vapor stream comprising hydrogen, hydrogen sulfide and hydrocarbons boiling in the diesel range, and a liquid hydrocarbonaceous stream comprising hydrocarbons boiling at and above the diesel range and saturated with hydrogen; (d) recycling at least a portion of the liquid hydrocarbonaceous stream produced in step (c) to the hydrocracking zone in step (b) as at least a portion of the liquid hydrocarbonaceous recycle stream; (e) fractionating in a fractionation zone at least a portion of the liquid hydrocarbonaceous stream produced in step (c) to produce a first stream of ultra low sulfur diesel and a stream comprising hydrocarbons boiling at a temperature above the diesel range; (f) recycling at least a portion of the stream comprising hydrocarbons boiling at a temperature above the diesel range produced in step (e) to the first hydrotreating reaction zone in step (a); (g) contacting the hydrocarbonaceous vapor stream from step (c) and a second hydrocarbonaceous feedstock comprising diesel boiling range hydrocarbons with a hydrotreating catalyst in a second hydrotreating reaction zone; and (h) fractionating at least a portion of the effluent from the second hydrotreating reaction zone to produce a second stream of ultra low sulfur diesel.
Other embodiments of the present invention encompass further details such as types and descriptions of feedstocks, hydrotreating catalysts and preferred operating conditions including temperatures and pressures, all of which are hereinafter disclosed in the following discussion of each of these facets of the invention.